DuckDuckGo is a lot more private than Ecosia. Ecosia only remove the last 2 bytes of the IP address when storing your request, DuckDuckGo stores none of it. Ecosia only fully anonymises it after 7 days, which is 7 days sooner than DuckDuckGo.

Ecosia is a very good cause, and I switched from DuckDuckGo because I wanted to help our environment. But it does come with a (albeit very small) privacy cost. DuckDuckGo, therefore, is much more private, and should be #1.